1. Field of the Invention
This invention relates generally to shaving devices, and more specifically to handles for wet shaving razors having biasing members and means to control creep in the biasing members.
2. Background Information
In recognition that skin surfaces to be shaved are not planar, some modern shaving implements, commonly known as disposable safety or wet shaving razors, have a handle and a pivotally connected razor cartridge that are intended to be permanently coupled and disposed of as a single unit. Other wet shaving razors include a disposable razor cartridge releasably connected to a reusable handle. The cartridge comprises a housing having at least one razor blade with a sharpened cutting edge disposed therein. During use, the razor cartridge can pivot relative to the handle about a pivot axis between a neutral, or at-rest, position and a rotated position. The handle is customarily provided with a biasing member that interacts with the razor cartridge to provide an at-rest position and to permit resilient pivotal movement of the razor cartridge away from the at-rest position in response to forces encountered during shaving. The bias force provided by the biasing member prevents chatter of the cartridge in use but is not so great to restrict or limit pivotal movement of the cartridge in response to the forces encountered during shaving.
The assignees of the present application successfully manufacture and sell a disposable wet shaving razor under the trademark XTREME3™. The XTREME3™ razor includes a handle assembly with a razor cartridge pivotally mounted thereon and a protective cap or cover that at least protects the cutting edges of the razor blades from accidental damage during transit. The XTREME3™ handle assembly and cartridge are generally disclosed in several U.S. patents to Richard et al including U.S. Pat. No. 6,138,361, essential matter of which is incorporated herein for reference. The XTREME3™ protective cap is generally disclosed in U.S. Pat. No. 5,893,213 to Motta, essential matter of which is incorporated herein for reference. The handle assembly of the XTREME3™ razor having reference numeral 94 in the '361 patent includes a pivot frame having reference numeral 103 therein. The handle assembly comprises three components: an upper and a lower housing permanently joined together and having the pivot frame permanently disposed therewithin. The pivot frame is manufactured by injection molding and comprises the thermoplastic material commonly known as acetal or more correctly polyoxymethylene or POM. POM is a so-called engineering grade thermoplastic and has excellent creep resistance characteristics. Creep is a commonly understood phenomenon that describes a permanent change of shape of a structure as a result of exposure to one or both of prolonged stress or prolonged elevated temperatures.
For at least manufacturing reasons it would be advantageous for the assignees of the present application to be able to manufacture at least a pivot frame or more preferably a unitary handle for a wet shaving razor from a commodity thermoplastic polymer such as polypropylene. Polypropylene offers many advantages including the ability to be chemically bonded to certain thermoplastic elastomer (TPE) materials. This ability enables the manufacturer to provide components having for instance a soft grip with relative ease by utilizing a two-shot or two-color injection molding process. In this process a relatively rigid polypropylene substrate can be provided with a whole or partial TPE skin having the desired soft grip characteristics. The TPE chemically bonds to the polypropylene at the interface between the two materials and generally no other attachment means are required. Unfortunately, commodity thermoplastic materials such as polypropylene have less desirable creep resistance characteristics than POM.
The object of the present invention is to provide, for manufacturing advantages, a wet shaving razor or component part thereof, manufactured from a commodity thermoplastic polymer and having means to control creep.